Left and Right operand of comma operator has no effect (Warning)

Question

I'm getting a warning in my constructor in my class, and I've never seen it before. This is what my constructor looks like.

    Account(std::string n = "NULL", std::string i = "0", Stats s = (0,0,1) ) 
        : name(n), id(i), stat(s) {}

If I remove any of these commas it results in a compile error, no? Is this warning incorrect, or is there something I can change to fix it?

Answer 1

The issue is this: (0,0,1).

That is parentheses around the expression 0,0,1, which evaluates to 1. (The comma operator is an infix operator that evaluates the first and second expression and returns the second. In this case, you have two such operators.)

I don't know what you wanted there, but I'm guessing that isn't it.

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EDIT: It seems you want Stats s(0,0,1).

Answer 2

The problem is most likely in that part Stats s = (0,0,1). C++ sees this as a sequence of expression to be computed while keeping only the last value. It returns 1. You probably mean

Stats s = Stats(0,0,1)

which works if your stats structure have such a constructor. Note that in C++11 you have this shorter syntax:

Stats s = {0,0,1}

Answer 3

I think what you are looking for is to give a default value to function argument which is a struct, and I think it was discussed here How can I assign a default value to a structure in a C++ function?